DC-to-DC converters are used in a wide variety of applications. However, one of the many problems that face these converters is sub-harmonic oscillations, which are oscillations in the output voltage and current. These sub-harmonic oscillations can damage equipment and make designing DC-to-DC converters difficult. The impact of sub-harmonic oscillations on the design of DC-to-DC converters is so substantial that there are numerous, recent research efforts to describe this phenomenon theoretically in the hopes of addressing it. Some of these articles describing the research into this phenomenon and into the development of models are as follows: Redl et al., “What a Design Engineer Should Know,” Proceedings Power Electronics Design Conference, pp. 18-33, 1985; Redl et al., “Superiority of Current-Mode Control for Stability Over a Wide Ranges of Output Capacitances and ESR,” Proceedings of Power Electronics Show and Conference, pp. 147-163, 1988; Redl et al., “Current-Mode Control, Five different Types, Used With the Three Basic Classes of Power Converters: Small-Signal AC and Classes Large-Signal DC Characterization, Stability Requirements, and Implementation of Practical Circuits,” 16th Annual IEEE Power Electronics Specialists Conference, pp. 771-785, 1985; Redl et al., “Near-Optimum Dynamic Regulation of DC-DC Converters Using Feedforward of Output Current and Input Voltage With Current-Mode Control,” IEEE Transactions on Power Electronics, Vol. PE-1, No. 3, pp. 191-192, July 1986; Redl et al., “Stability Analysis of Constant-Frequency Current-Mode Controlled Switching Regulators Operating Above 50% Duty Ratio,” 13th Annual IEEE Power Electronics Specialists Conference, pp. 212-223, 1982; Redl et al., “Overload-Protection Methods for Switching-Mode DC/DC Converters: Classification, Analysis, and Improvements,” 18th Annual IEEE Power Electronics Specialists Conference, pp. 107-118, 1987; Redl et al., “Instabilities in Current-Mode Controlled Switching Voltage Regulators,” 12th Annual IEEE Power Electronics Specialists Conference, pp. 17-28, 1981; Ceisch, Cecil W., “Simple Switching Control Method Changes Power Converter into a Current Source,” 9th Annual IEEE Power Electronics Specialists Conference, pp. 300-306, 1978; Ridley, Raymond, “Current Mode or Voltage Mode,” Switching Power Magazine, pp. 4, 5, and 9, October 2000; Ridley, Raymond, “Current Mode Control Modeling,” Switching Power Magazine, July 2001; Ridley, Raymond, “Six Common Reasons for Power Supply Instability,” Switching Power Magazine, Vol. 3, No. 3, pp. 6-13, July 2002; Ridley, Raymond, “Loop Gain Crossover Frequency,” Switching Power Magazine, pp. 22-27, January 2001; Ridley, Raymond, “Loop Gain Measurement with Current Injection,” Switching Power Magazine, Vol. 4, No. 2, pp. 27-30, May 2003; Sheehan, Robert, “Current-Mode Modeling for Peak, Valley and Emulated Control Methods,” National Semiconductor; and Sheehan, Robert, “Emulated Current Mode Control for Buck Regulators Using Sample-and-hold Technique,” Power Electronics Technology Exhibition and Conference, October 2006. None of these articles propose, though, feasible solutions for both continuous and discrete Conduction-Mode operation. As a matter of fact, one of the more recent articles states that “[p]eaking of the closed loop gain due to insufficient slope compensation and ripple on the control voltage can cause sub-harmonic oscillation before the calculated limit, i.e. at duty cycles below 0.5 for peak current mode,” indicating the persistence of the problem. Sheehan, Robert, “Emulated Current Mode Control for Buck Regulators Using Sample-and-hold Technique,” Power Electronics Technology Exhibition and Conference, October 2006.
Clearly, the effort and expense aimed at understanding sub-harmonic oscillations in DC-to-DC converters establishes that there is a long felt need to solve this problem. To date, however, no amenable solution has been developed. This is not to say that others have not attempted to reduce the effect of sub-harmonic oscillations; others have tried and failed. According to a well-known and well-respected consultant and expert in the power electronics industry, Dr. Raymond Ridley, many others have tried and failed. Specifically, Dr. Ridley in an article in Switching Power Magazine from October 2000 explains that:                [m]any IC manufacturers have attempted to place all the power supply functions on a single chip, including the current sensing and filtering[, but] . . . they have often found the current-mode noise problems insurmountable and have converted to voltage-mode control . . . [, losing] all inherent advantages of current mode.Ridley, Raymond, “Current Mode or Voltage Mode,” Switching Power Magazine, pp. 4, 5, 9, October 2000.        
One conventional arrangement is shown in U.S. Pat. Nos. 7,372,238; 7,372,238; 7,045,993; and 7,119,522 by Tomiyoshi. This arrangement employs a sample-and-hold circuit with a DC-to-DC converter, but the sample-and-hold circuit operates almost independently of a clock or oscillator. By not using the clock or oscillator signal, it is more difficult to be able to anticipate switch actuation, which could lead to continued sub-harmonic oscillations. Additionally, a COMP or voltage divided output signal is not sampled; instead, the current across the low-side FET is sampled, which indicates that the circuit of Tomiyoshi would be vulnerable to noise and interference with actuation of the high-side FET. Thus, Tomiyoshi would still exhibit sub-harmonic oscillations stemming from actuation of the high-side FET.
As a result of the research and development efforts to explain and reduce the effects of sub-harmonic oscillations in DC-to-DC converters, there is need for a method and/or apparatus that addresses this phenomenon.